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Email Marketing Client

High-Throughput Email Verification

Custom Rust SMTP engine with sub-second verification processing millions of emails

82 Lambda functions

Rust SMTP engine

Sub-second speedMillions verified
Email verification case study — high-volume real-time SMTP and DNS verification pipeline with 95%+ deliverability accuracy

Context

An email marketing business needed high-volume email verification to protect sender reputation and reduce bounce rates. Existing services were too slow and inaccurate.

Constraint

Sub-second response times required at scale. Must handle full SMTP handshake without sending actual emails. Sender reputation had to be protected.

Intervention

Built a custom Rust SMTP engine on 82 Lambda functions with connection pooling, retry logic, and multi-factor quality scoring beyond valid/invalid.

Outcome

Millions of emails verified at sub-second speed, multi-factor quality scoring, fully serverless - delivered in 30 weeks.

Architecture

From bulk ingestion to verified, scored email lists

Bulk Ingestion

High-throughput intake pipeline processes email lists of any size. Deduplication, format validation, and domain extraction happen before verification begins.

Rust SMTP Engine

Custom-built Rust engine handles SMTP verification at scale with sub-second response times. Connection pooling, retry logic, and rate limiting ensure deliverability without triggering spam filters.

Lambda Orchestration

82 Lambda functions manage the verification pipeline - from DNS lookups and MX record resolution through SMTP handshake verification and result aggregation.

Quality Scoring

Multi-factor scoring classifies emails as valid, invalid, risky, or unknown. Catch-all detection, disposable email filtering, and role-based address identification.

Tech Stack

Core Engine

Custom Rust SMTP engine

Compute

AWS Lambda (82 functions)

Languages

Rust, Python, TypeScript

Architecture

Fully serverless on AWS

Performance

Sub-second verification

Scale

Millions of verifications processed

Results

82

Lambda functions

Rust

Custom SMTP engine

Sub-second

Verification speed

Millions

Emails verified

Full SMTP

DNS → MX → mailbox handshake

Multi-factor

Quality scoring

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